The present invention relates to refrigerant compressors of the scroll type. More particularly, the present invention relates to a discharge check valve arrangement in a scroll compressor in which the valve element is maintained open and is generally unaffected by the momentary gas backflow and/or pressure pulses that can occur during normal compressor operation, yet moves to close the discharge port quickly upon compressor shutdown so as to protect the compressor against high speed and prolonged reverse direction scroll rotation and the damage resulting therefrom.
Scroll compressors are compressors having tw4o interleaved scroll wraps extending from opposing end plates which, when the compressor is in operation, undergo relative orbital motion with respect to each other. When such rotation is in the appropriate direction, suction pockets form at the outer periphery of the interleaved scroll wraps, fill with suction gas, close off and are displaced radially inward, decreasing in size until they join and form a discharge pocket out of which compressed gas is expelled into the discharge pressure portion of the compressor shell.
There is a need to isolate the scroll set from the backflow of compressed gas out of the discharge pressure portion of the compressor shell that would otherwise occur when the compressor is shutdown and is no longer driven by its motor. Absent means to quickly isolate the scroll set from the discharge pressure portion of the compressor shell at compressor shutdown, the backflow of compressed gas there out of will cause the scroll set to be driven in a reverse direction at relatively very high speeds in a free-wheeling fashion for a relatively prolonged period of time. Such high speed reverse rotation can damage or destroy the compressor for lack of bearing lubricant or for lack of bearings designed to accommodate scroll rotation at the speeds that a discharge gas-driven scroll member can attain.
A common problem associated with discharge check valve arrangements is the sticking open or unresponsiveness of the valve element of the valve assembly to closure as a result of the valve element's becoming coated with oil and sticking to its seat. In that regard, discharge gas issuing from a scroll set into the discharge pressure portion of the shell of a scroll compressor will carry a small amount of oil entrained within it. Such oil is picked up by the gas that undergoes compression in the scroll set as a result of the passage of that gas through the suction pressure portion of the compressor shell during the course of its travel to the scroll set. Oil is picked up in such travel because the suction pressure portion of such compressors often acts as a sump for oil used to lubricate moving components of the compressor that are located in its suction pressure portion.
Although relatively very small in amount, much of the oil entrained in the compressed gas issuing from the scroll set through the discharge port is disentrained therefrom by its impact with the compressor's discharge check valve assembly. As such, the discharge check valve assembly will typically be oil-coated when the compressor is in operation. Discharge check valve arrangements must, however, be such that the valve element of the arrangement is not prone to sticking open as a result of the adhesive forces that exist between it and its seat as a result of their being oil-coated.
Protection against discharge gas backflow upon compressor shutdown has most typically been accomplished by the installation of a simple check valve arrangement directly over the compressor's discharge port within the discharge pressure portion of the compressor shell. The valve element of the arrangement is forced open or away from the discharge port by the flow of discharge gas from the scroll set. The valve element is carried or urged shut by gravity, spring action and/or with the assistance of the reverse flow of discharge gas out of the discharge pressure portion of the compressor shell back to the scroll set that occurs upon compressor shutdown. Such valve arrangements, in addition to being susceptible to sticking open, can be prone to chattering as a result of the momentary gas backflow pulses that are repetitively created in the discharge pressure portion of the compressor shell while the compressor is in operation. Such chatter creates noise and causes both the valve element and its seating surface to wear.
U.S. Pat. No. 4,820,130, assigned to the assignee of the present invention, focuses on discharge check valve matters but is representative of a fairly complex arrangement having functions other than the discharge check valve function. It is, however, generally explanatory of the need for a discharge check valve in a scroll compressor.
A more recent patent which describes a check valve arrangement is U.S. Pat. No. 5,451,148. The focus of the '148 patent is the provision of a valve element in a discharge check valve arrangement which is not susceptible to sticking open as a result of the adhesion of the valve to its seal due to the oil film which will coat compressor components in the vicinity of the discharge port. That patent is commended to the reader for its teachings with respect to discharge check valves and their use in scroll compressors in general. The patent focuses, however, on a check valve element which is of a specific and relatively complex geometry.
Also of interest is relatively recent U.S. Pat. No. 5,494,422. That patent is directed, among other things, to the problem of overcoming the sticking of the valve element in a discharge check valve arrangement in a scroll compressor in the open position as a result of its being oil-coated and adhering to the valve stop. In the arrangement of the '422 patent, the edge of the valve element appears to remain fully exposed to the flow of discharge gas when the compressor is in operation. While it may not be susceptible to sticking, it does appear to be susceptible to valve chatter due to its exposure, about its periphery, to the normal and repetitive backflow pulses that are created is the discharge pressure portion of the compressor shell by the normal operation of the compressor.
There is a need for an improved discharge check valve arrangement in a scroll compressor which is insensitive to the normal gas backflow pulses and/or pressure pulsations that can be repetitively created during the normal operation of a scroll compressor, is therefore not susceptible to chattering, is not prone to sticking open due to the adhesive forces of oil which coats the valve apparatus when the compressor is in operation and which is immediately responsive to the de-energization of the compressor to close the discharge port off from gas backflow so as to prevent the possible damage or destruction of the compressor due to the flow of discharge gas out of the discharge pressure portion of the compressor shell to the scroll set and the consequent high speed, reverse direction rotation of a scroll member.